The work is nicely done. But each time I see a website presenting a book content or catalog in pages like that, like if it was a real book, it really pisses me off. It is a design move that goes against ergonomy. Harder/slower to browser, harder/slower to seek, you have to do a mental break while pages are changing with effect that does not get the same efficiency feeling than a real book.
Tap/swipe/arrows to turn really switches my brain. And the fact that the goal of this library is to allow native support for everything else for the entire book (like find, etc) really makes this feel like using the Kindle app or the Apple Books app. It's the first time I thought to myself, "no, I wouldn't need to download the ePub and put it on Dropbox so that I can easily import it to my favorite eBook app. The html version is great."
What I didn't notice is if your page number is captured in the url or not (again, because I'm on mobile). That seems like an important feature.